1. Field of the Invention
The field of the present invention is improvements in engine parts provided with manifold type exhaust passages and more particularly is improvements in such engine parts as comprising a cast main body and a manifold type ceramic liner cast within the main body to define a manifold type exhaust passage, the ceramic liner including a hollow cylindrical liner body and a plurality of cylinder members branched from the liner body.
2. Description of the Prior Art
As engine parts of the mentioned type, there has conventionally been known one disclosed in Japanese Patent Application Laid-open No. 111985/1984, for example.
An engine part having a ceramic liner of the mentioned type used therein tends to be heated excessively during engine operation due to an exhaust gas of a high temperature passing through the cylinder members, at a branched area of the ceramic liner where adjacent cylinder members are branched apart. It is preferable to reduce the radius of the inside surface of the branched area to a possible extent in case the high temperature exhaust gas within the cylinder members should be guided smoothly toward the liner body. This is difficult in the aspect of molding and therefore there remains a demerit that an exhaust gas of a high temperature is liable to stay on the inner surface side of the branched area.
As a result, thermal stress is concentrated on the branched area and this leads to a problem that cracks tend to occur at the branched area since conventional engine parts have not been equipped with specific means for moderating or reducing concentration of such thermal stress.
There is also a problem that the flowing property of molten metal at the time of casting the main body is not good at the branched area since the molten metal is cooled by the ceramic liner and a core member.